Chemical compound useful as intermediate for preparing a catechol-o-methyltransferase inhibitor

ABSTRACT

There is disclosed a methylated intermediate which may be demethylated to provide an inhibitor of catechol-O-methyltransferase useful in the treatment of Parkinson&#39;s disease. Also disclosed are methods of making and using said intermediate.

FIELD OF THE INVENTION

The present invention relates to a novel compound and to processes whichemploy it in the preparation of a catechol-O-methyltransferaseinhibitor. In particular this invention relates to5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzenewhich can be used in the process for the preparation of5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-3-nitrobenzene-1,2-diol.

BACKGROUND TO THE INVENTION

A preferred method of treatment of Parkinson's disease is theadministration of a combination of levodopa and a peripherally selectivearomatic amino acid decarboxylase inhibitor (AADCI) together with acatechol-O-methyltransferase (COMT) inhibitor. The currently employedCOMT inhibitors are tolcapone and entacapone. However, some authoritiesbelieve that each of these COMT inhibitors have residual problemsrelating to pharmacokinetic or pharmacodynamic properties, or toclinical efficiency or safety. Hence, not all patients get most benefitfrom their levodopa/AADCI/COMT inhibitor therapy.

Favoured new COMT inhibitors were disclosed in L. E. Kiss et al, J. Med.Chem., 2010, 53, 3396-3411 (D1), WO 2007/013830 (D2) and WO 2007/117165(D3) which are believed to have particularly desirable properties sothat patients can benefit from enhanced therapy.

D1, D2 and D3 also disclosed methods of preparing the new COMTinhibitors. Those processes, although effective, would benefit from anincrease in yields. Other benefits which would be appropriate includethose selected from reduction in number of process steps, reduction innumber of unit operations, reduction of cycle-times, increased spaceyield, increased safety, easier to handle reagents/reactants and/orincrease in purity of the COMT inhibitor, especially when manufacture oflarger quantities are envisaged. A process has now been discovered thatproceeds via a new intermediate which is suitable for manufacture ofcommercially useful quantities of a particularly apt COMT inhibitor ingood yield. Additional benefits occur such as those selected from areduced number of process steps and number of unit operations, reducedcycle-times, increased space yield, increased safety, with easier tohandle reagents/reactants, improved impurity profile and/or good purity.

BRIEF DESCRIPTION OF THE INVENTION

The present invention in one aspect provides5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzeneand salts thereof, that is the compound of the formula (I):

and salts thereof.

Most aptly the compound of formula (I) is unsalted. However, salts ofthe hydroxy group with metal ions such as the alkali or alkaline earthmetals, particularly the sodium and potassium salts are provided as wellas those of highly basic organic compounds such as guanidine or thelike.

Particularly suitably the compound of formula (I) or its salt isprovided in a form suitable for use as a chemical intermediate. This maybe, for example, in a form at least 50% pure, in crystalline form, insolid form or in an organic solvent or the like.

The compound of formula (I) is useful as an intermediate in thepreparation of5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-3-nitrobenzene-1,2-dioli.e. the compound of formula (II):

The compound of formula (II) may also be referred to as opicapone or2,5-dichloro-3-(5-(3,4-dihydroxy-5-nitrophenyl)-[1,2,4]-oxadiazole-3-yl)-4,6-dimethylpyridine-1-oxide.Opicapone has been found to be more potent than tolcapone in inhibitingliver COMT both at 3 hours and 6 hours post oral administration to rats[ED₅₀ in mg/kg, opicapone 0.87 at 3 hours and 1.12 at 6 hours ascompared to tolcapone 1.28 at 3 hours and 2.08 at 6 hours]. Opicapone ata dose of 3 mg/kg was found to be more effective at inhibiting rat liverCOMT with nearly complete inhibition occurring 2 to 6 hours post oraladministration with only about 90% of enzyme activity recovered after 72hours while tolcapone provided shorter duration of activity with about84% recovery after only 9 hours. Both opicapone and tolcapone inhibithuman recombinant S-COMT but opicapone has an inhibitory constant of 16pM being 10 fold lower than that for tolcapone. With respect to thedesirable property of avoiding inhibition of COMT in the brain,opicapone following oral administration to the rat was found to bedevoid of effect whereas tolcapone inhibited about 50% of enzymeactivity over a period of 8 hours post administration.

In a further aspect the invention provides a process for the preparationof the compound of the formula (II) as set forth above or a salt thereofwhich comprises the demethylation of a compound of the formula (I) asset forth above or a salt thereof. In one embodiment, the process doesnot require compound of the formula (I) to be dried for the subsequentdemethylation reaction, i.e. compound of the formula (I) may be wet withtoluene.

Typically, the amount of toluene in compound of the formula (I) is inthe range 1% to 60% w/w. This is advantageous as it improves the processtime and safety. In another embodiment, the process does not require thecompound of the formula (II) to be slurried in EtOH. This isadvantageous as it improves the process cycle-time.

Most aptly the process is adapted to the preparation of a compound ofthe formula (II) but salts thereof may be prepared, for example analkali metal or alkaline earth metal salt, preferably the sodium orpotassium salt, or a salt of a strongly basic organic compound such as aguanidine.

The O-demethylation reaction may be effected by reaction with ademethylating reagent. A suitable demethylating reagent is a Lewis acidin the presence of appropriate base, for example, aluminium chloride(AlCl₃) and pyridine. The demethylation will generally be performed at amoderately elevated temperature, preferably between 45° C.-70° C., morepreferably between 55° C.-65° C.

The compound of the formula (II) prepared by this process can besufficiently pure for use in a pharmaceutical composition for use in thetreatment of Parkinson's disease as hereinbefore indicated. The thusprepared compound of formula (II) may be ball milled or otherwiseprovided in microparticulate form, for example micronized through jetmills (MC JETMILL®). Thus, in a further aspect of the invention providesa pharmaceutical composition which comprises a compound of formula (II)in microparticulate form for use in the treatment of Parkinson's diseaseby oral administration.

It is a particular advantage of the present process that the product ofthe reaction of the compounds of formulas (IV) and (V) obtained afterprecipitation with ethanol may be employed without the need forisolation of crude compound of formula (III) as the work-up procedureallows the isolation of compound of formula (III) with a purity not lessthan 95% (HPLC), preferably not less than 96% and ready to use in thenext stage of the synthesis. Another advantage of the present process isthe optional ability to omit the isolation of any intermediate compoundsof the reaction of the compounds of formulas (IV) and (V).

In one embodiment, the acyl chloride may be prepared by the reaction ofthe compound of formula (VI):

with SOCl₂ in dioxane at 75° C.-85° C. The use of dioxane in this stagefacilitates ease of use in subsequent reactions, for example if itoccurs in a solvent system containing dioxane (no need for solvent swapbefore proceeding with the next step), allows a higher space yield,higher process output, requires less reaction vessels, shorter reactiontimes, improved solubility of reactants (homogeneous reaction solutionsmixture instead of a slurry) and avoids the use of DMF (increasedpurity).

In another embodiment, the reaction of compound of formula (VI) withSOCl₂ is performed in DCM in the presence of a catalytic amount of DMFat 35-50° C., preferably at reflux temperature.

When preparing the compound of formula (II) in a form for use in apharmaceutical composition, it may be recrystallized from propan-2-oland formic acid and thereafter ball milled or micronized through spiraljet mills to provide particles of the desired size for good oralbioavailability and/or suitable properties (e.g. suitable particle size)for the preparation of a pharmaceutical composition.

BRIEF DESCRIPTION OF THE FIGURES Acronyms List DMF—DimethylformamideSOCl₂—Thionyl Chloride MeOH—Methanol THF—Tetrahydrofuran

DMAc—Dimethyl acetamideTFAA—Trifluoroacetic acid anhydride

-   IPA—Isopropoanol-   HNO₃—Nitric acid-   DCM—Dichloromethane-   EtOH—Ethanol-   HCl—Hydrochloric acid-   UHP—Urea Hydrogen Peroxide-   AlCl₃—Aluminium trichloride-   NMP—N-methylpyrolidone-   POCl₃—Phosphoryl chloride-   (CH₃)₄NCl—Tetramethylammonium chloride

FIG. 1. Process to prepare compound of formula (II) using compound offormula (I) as an intermediate according to one embodiment of theinvention.

1. nitric acid 65%, acetic acid, 10-20° C., recrystallization; 2. SOCl₂,DMF (catalytic), 50° C.; 3. 50% hydroxylamine in water, catalytic amountof 1,10-phenantroline hydrate, MeOH, 75-80° C.; 4. THF, DMAc, pyridine,110-120° C.; 5. TFAA, DCM, UHP, 10-20° C.; 5a. solvent swap from DCM toacetonitrile; 5b. crystallization from toluene/formic acid; 6. aluminiumchloride, pyridine, N-methylpyrrolidone; 6a. Ethanol reslurry; 6b.Re-crystallization from IPA/formic acid.

FIG. 2. Process to prepare compound of formula (II) using compound offormula (I) as an intermediate according to one embodiment of theinvention.

1. 50% NH₂OH in water, catalytic amount of 1,10-phenantroline hydrateMeOH; 2. 65% HNO₃, acetic acid, 2a. Re-crystallization from acetic acid;3. SOCl₂, DCM, DMF (catalytic), solvent switch from DCM to THF, additionof acid chloride to amidoxime in DMAc, addition of pyridine, heat to110° C.; Quench on aq. HCl and DCM; crystallization from DCM/EtOH; 4.DCM, UHP, TFAA, solvent switch from DCM to toluene/formic acid;crystallization from toluene/formic acid; 4a. Re-crystallization fromformic acid/toluene; 5. AlCl₃, NMP, pyridine, the compound of formula(II) is precipitated and isolated by addition of diluted HCl; 5a.Re-crystallization from IPA/formic acid.

FIG. 3. Process to prepare compound of formula (II) using compound offormula (I) as an intermediate according to one embodiment of theinvention.

1. morpholine in MeOH; 2. SOCl₂ in acetonitrile; 3. POCl₃, (CH₃)₄NCl inDCM; 4. 50% NH₂OH in water, catalytic amount of 1,10-phenantrolinehydrate, MeOH; 5. 65% HNO₃, acetic acid, 5a. Re-crystallization fromacetic acid; 6. SOCl₂, DCM, DMF (catalytic), solvent switch from DCM toTHF; 6a. addition of acid chloride to amidoxime in DMAc, addition ofpyridine, heat to 110° C.; precipitation of DMAc solution aq. HCl withisolation of crude compound of formula (III); crystallization fromDCM/EtOH; 7. DCM, UHP, TFAA, solvent switch from DCM to toluene/formicacid; crystallization from toluene/formic acid; 7a. Re-crystallizationfrom formic acid/toluene; 8. AlCl₃, NMP, pyridine; the compound offormula (II) is precipitated and isolated by addition of diluted HCl,8a. reslurry in ethanol 8b. Re-crystallization from IPA/formic acid.

FIG. 4. Process to prepare compound of formula (II) using compound offormula (I) as an intermediate according to one embodiment of theinvention.

1. 50% NH₂OH in water, catalytic amount of 1,10-phenantroline hydrateMeOH; 2. 65% HNO₃, acetic acid, 2a. Re-crystallization from acetic acid;3. SOCl₂, dioxane, addition of acid chloride to amidoxime in dioxane,addition of pyridine, heat to 110° C.; Quench on aq. HCl and DCM;crystallization from DCM/EtOH; 4. DCM, UHP, TFAA, solvent switch fromDCM to toluene/formic acid; crystallization from toluene/formic acid;4a. Re-crystallization from formic acid/toluene; 5. AlCl₃, NMP,pyridine; the compound (II) is precipitated and isolated by addition ofdiluted HCl; 5a. Re-crystallization from IPA/formic acid.

FIG. 5. Process to prepare compound of formula (II) using compound offormula (I) as an intermediate according to one embodiment of theinvention.

1. morpholine, MeOH, 2. SOCl₂, 3. POCl₃; 4. H₂NOH, 1,10-phenantroline;5. HNO₃, acetic acid; 6. recrystallization from acetic acid; 7. SOCl₂,1,4-Dioxane; 8a. 1,4-Dioxane, Pyridine; 8b. EtOH; 9. DCM, UHP, TFAA; 10.toluene, formic acid; 11. AlCl₃, NMP, Pyridine; 12. Formic acid/IPA.

FIG. 6. Process to prepare compound of formula (II) using compound offormula (I) as an intermediate according to one embodiment of theinvention.

1. morpholine, MeOH, 22 h, reflux; 2a. SOCl₂, MeCN; 2b. 2 h, 65° C.; 2c.2 h, 20° C.; 3. POCl₃, TMACl, 8 h, 110° C.; 4. NH₂OH/H₂O,1,10-phenantroline monohydrate, MeOH, 6 h, 75° C.; 5. HNO₃, HOAc, 10-20°C.; 6. SOCl₂, DCM/DMF, 8 h, 40° C.; 7. DMA/THF, 2 h, 5-10° C.; 8.Urea-H₂O₂, DCM/TFAA, 18 h, 20° C.; 9. AlCl₃, NMP/Pyridine, 2 h, 60° C.;10. Recrystallization.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides the compound of the formula (I):

and salts thereof.

The use of the compound of formula (I) leads to a particularly effectiveprocess for the preparation of the compound of formula (II). By avoidingthe deprotection of both phenolic hydroxyl groups of prior artprocesses, good yields may be achieved when starting from the readilyavailable and relatively less expensive compound vanillic acid.

The compound of formula (I) may be obtained in high purity, for examplein crystalline form, which also helps achieve the preparation of thecompound of formula (II) in highly pure forms, for example containingonly very low amounts of impurities.

Aptly, the compound of formula (I) is crystallised and/or recrystallizedfrom a mixture of organic solvents one of which is an acid, favourablyformic acid. A preferred recrystallization solvent for the compound offormula (I) is a mixture of toluene and formic acid. Another preferredrecrystallization solvent system for the compound of formula (I) isformic acid/isopropanol (solvent/antisolvent).

The compound of formula (I) or salt thereof may be prepared by theoxidation of the compound of the formula (III):

or salt thereof.

Normally and preferably the unsalted compound of formula (I) is preparedfrom a compound of formula (III) but if a salt is required this may beproduced by reaction of the phenolic hydroxyl group with an appropriatebase after the formation of the compound of the formula (I).

The oxidation reaction may be performed with any suitable oxidizingagent but preferably a peroxide is employed. Suitably the peroxide maybe H₂O₂ which is preferably employed as H₂O₂-urea addition complex. Theoxidation is preferably carried out in the presence of an organic acidanhydride such as trifluoroacetic anhydride.

The oxidation generally takes place in a non-hydroxylic organic solvent,preferably in halogenated solvents such as methylene chloride. Theoxidation is preferably performed at between 15° C. and 30° C., morepreferably from 20° C.-25° C.

The compound of formula (III) may be prepared by the reaction of acompound of formula (IV) wherein Y is a halo group, such as chloride, orOR in which R could be hydrogen or a C1-C6 alkyl such as methyl orethyl:

with a compound of the formula (V):

The reaction of the compounds of formula (IV) and (V) can take place inan organic solvent and more generally in a mixture of organic solventsat least one of which will be basic solvent, for example pyridine. Asuitable mixed solvent is dimethylacetamide, tetrahydrofuran andpyridine. Alternatively, the solvent organic mixture is a mixture ofdioxane and pyridine. The reaction of the compounds of formula (IV) and(V) can also take place in the presence of an organic base such aspyridine or a tertiary amine. When Y is OR and R is hydrogen in thecompound of formula (IV), the compound has formula (IX):

When Y is OR and R is hydrogen in the compound of formula (IV), theaddition of a coupling reagent such as carbodiimide, phosphonic acidderivatives, carbonyl diimidazole derivatives is required.

When Y is OR and R is C1-C4 alkyl such as methyl, the addition of aLewis acid such as aluminium trichloride, or a Brönstedt acid such asp-Toluene sulfonic acid catalyst may be required.

When Y is a chloride, compound of formula (VIII), may be preferably usedto prepare the compound of formula (III).

The cyclization process will take place at an elevated temperature, forexample at 100° C.-120° C. Particularly the process will be performed at105° C.-115° C.

If desired a further organic liquid such as ethanol may be added at theend of the reaction. Suitably precipitation is not effected by theaddition of such a further organic liquid.

The reaction of the compounds of formulas (IV) and (V) is believed toproceed via the open chain intermediate shown below:

It is an advantage of the present process that this intermediate neednot be isolated but becomes cyclised to the desired compound of formula(III) under the reaction conditions employed. Suitably the reaction isperformed at a temperature of between 100-120° C. to give the desiredcyclised compound of formula (III).

The use of the compound of formula (VIII) has been found to lead toenhanced yields in comparison with other activated analogues such asthose formed from the acid and coupling reagents.

In one embodiment of the present invention the compound of formula (V)is prepared from the compound of the formula (VII)

by reaction with hydroxylamine in the presence of 1,10-phenanthrolinemonohydrate. Preferably the reaction is carried in a mixture of methanoland water at 70-80° C. Conveniently, the presence of 1,10-phenanthrolinemonohydrate reduces or eliminates the formation of unwanted amide andfavours the formation of the wanted amidoxime of formula (V).

The compound of formula (IV) may be prepared from the correspondingcarboxylic acid by esterification or formation of an acid chloride.Aptly for preparing an acid chloride this may involve reaction withSOCl₂. Such corresponding acid may be prepared by nitration of vanillicacid. Compounds of Formula (IV) which are esters may also be prepared bynitration of the corresponding ester of vanillic acid, for example bynitration of the methyl ester of vanillic acid. Suitable conditions forsuch reactions are set forth in the Examples hereinafter.

The compound of formula (II) in crystalline form is particularly apt foruse in pharmaceutical compositions for administration orally. Inparticular, such compositions may be in the form of discrete unit dosessuch as tablets or capsules.

The pharmaceutical composition which contains the compound of formula(II) in crystalline form, preferably prepared as described herein, willalso comprise a carrier therefor. Suitable carriers include thosedescribed in D1, D2 or D3, referred to hereinbefore. The pharmaceuticalcomposition which contains the compound of formula (II) in crystallineform may additionally comprise levodopa (L-DOPA) and/or a peripherallyselective aromatic L-amino acid decarboxylase inhibitor (AADCi).

The compound of formula (II) in crystalline form or pharmaceuticalcompositions thereof may be used to treat some central and peripheralnervous system disorders, such as Parkinson's disease, mood disorders,restless legs syndrome, gastrointestinal disturbances, edema formationstates and hypertension. This may be by the administration to a patientin need thereof levodopa, a peripherally selective aromatic amino aciddecarboxylase inhibitor and the crystalline compound of formula (II).Such administration is preferably oral administration and employs adiscrete unit dose such as a tablet or capsule.

The crystalline compound of formula (II) employed in such compositionsis preferably microparticulate, for example as formed by ball milling orby micronization through spiral jet mills. Suitable micronization may becarried out with MCJETMILL® type 200 milling equipment. Suitably the D10(EDC (equivalent circle diameter)) is not less than 3, 4, 5 or 6 μm (forexample not less than 4 μm), the D50 (EDC) is 5-50, 10-45, 15-30 or20-25 μm (for example 10-45 μm) and the D95 (EDC) is not more than 60,70, 80 or 90 μm (for example not more than 90 μm). More suitably the D10(EDC) is not less than 4 or 5 μm (for example not less than 5 μm), theD50 (EDC) is 10-45 or 15-30 μm (for example 15-30 μm) and the D95 (EDC)is not more than 60 or 70 μm (for example not more than 60 μm).

The following preparations describe an apt process for the preparationof useful intermediates. The following Examples illustrate processes andproducts according to the invention. These Examples are non-limiting andmay be modified in accordance with the description herein and theknowledge of the skilled person.

Preparation of Intermediates Preparation 1

Cyanoacetamide (280 g) was reacted with acetyl acetone (352.9 g) inmethanol (1015 g) and morpholine (14.9 g). The reaction was stirredunder reflux at 65° C. until the reaction appeared complete. Theresulting product suspension was filtered, washed with methanol anddried to provide the desired product about 97% yield.

Preparation 2

The product of Preparation 1 (159 g) was suspended in acetonitrile(749.5 g) and cooled to 0-5° C. Sulfuryl chloride (178.9 g) was addedand the reaction mixture warmed to room temperature and stirred untilthe reaction appeared complete.

The resulting suspension is cooled to 0-5° C. and filtered. The solidwas washed with acetonitrile, ethyl acetate and heptane. The product wasthen dried under vacuum at 50° C. to yield the desired product (82%).

Preparation 3

Phosphoryl chloride (973.2 g), tetramethylammonium chloride (67.3 g) andcompound of Preparation 2 (227.1 g) were added to dichloromethane (500g). The suspension was heated to 85° C. and stirred for 5 hours. Excessof phosphoryl chloride was removed by distillation in vacuo. Thereaction mixture was cooled below 30° C. and diluted withdichloromethane. The resulting solution was added to water (1350 g) atroom temperature and stirred for 30 minutes. The lower organic phase wasseparate and the aqueous phase extracted with dichloromethane. Theorganic phases were combined, washed with water and then treated withcharcoal. The charcoal was filtered and a solvent swap to heptane wasperformed by distillation at atmospheric pressure. The solution wasfiltered at 50° C. and then cooled to 30° C. On further cooling to 0° C.crystals were obtained. These were isolated by filtration, washed twicewith heptane. After drying at 50° C. the desired product was obtainedtypically at 88-91%.

The above process was repeated with a reduction in dichloromethaneduring crystallisation and adding some methanol. The resultingplate-like crystals were more easily transferred for subsequent use.

Preparation 4a

Product of Preparation 3 (68.6 g) and 1,10-phenanthroline monohydrate(0.9 g) were suspended in methanol (240 g) at room temperature. Water(518 g) and a hydroxylamine solution (50% in water, 80.9 g), were addedand the mixture heated to 70-80° C. and stirred for 5-6 hours. Water wasadded at 70-80° C. and the solution held for 1 hour to inducecrystallization. Crystallization was completed by cooling to 15° C. over8 hours. The product was filtered off and washed twice with water anddried at 50° C. under vacuum. The product was an off white to lightyellow and the yield was 87.9%.

Preparation 4b

A suspension of 2,5-Dichloro-4,6-dimethyl-nicotinonitrile (45.0 kg) and50% hydroxylamine (59.2 kg) in the presence of catalytic amount of1,10-phenanthroline monohydrate (0.680 kg) in methanol/water (214 kg/362kg) is heated to 70-80° C. The mixture is agitated at 70-80° C. Water(353 kg) is added slowly into the resulting solution while thetemperature is maintained at >79° C. The solution is cooled to 75° C.with stirring resulting in crystallization of(Z)-2,5-dichloro-N′-hydroxy-4,6-dimethylnicotinimidamide. The suspensionis further cooled to 20° C., the solid is filtered off and the wet cakeis washed with water (160 kg).(Z)-2,5-dichloro-N′-hydroxy-4,6-dimethylnicotinimidamide is dried undervacuum at max. 60° C. until residual water level is max 0.15% (KF).

Example 1a Preparation of 4-hydroxy-5-methoxy-3 nitrobenzoic acid

Vanillic acid (75 g) was suspended in acetic acid (788 g). Thesuspension was cooled to 10° C. to 15° C. and nitric acid (49 g or 65%solution) was added over three hours at a rate which kept temperaturebetween 10° C. and 20° C. The resulting yellow orange was stirred for afurther one hour at 18° C. to 23° C. The suspension was filtered off,washed with acetic acid, then a mixture of acetic acid and water (1/2)and then water. Yield of 53% of a 87.9% pure product was obtained.

The above crude product was suspended in acetic acid and warmed to 105°C. to 110° C. until an orange brown solution is obtained. The solutionwas transferred to the crystallization vessel via a charcoal filter (orpolish filtration) at a temperature above 85° C. (optional step). Thesolution was then cooled to 80° C. to 85° C. The mixture was stirred forone hour at 70° C. to 80° C. (optionally at 75° C.) during whichcrystallization occurred. The product suspension was cooled to 20° C. to25° C. for 17 hours or stirred for at least 12 h at 20° C. to 25° C. Theproduct suspension was filtered and washed with acetic acid, then aceticacid/water (1/2) and finally water. The product was dried under vacuumat 50° C. to 55° C. The yield of 70% corresponds to an overall yield of44% for both parts of this preparation. The purity of the productassayed at 99.7%.

The preceding crystallization step is optional and the solution may betransferred to the crystallization vessel via polish filtration insteadof via a charcoal filter.

The post crystallization suspension may be stirred for at least 12 hoursat 20° C. to 25° C. as an alternative to 17 hours.

Example 1b Preparation of 4-hydroxy-5-methoxy-3 nitrobenzoic acid

A reactor was charged with 525 kg of glacial acetic acid and 50 kgvanillic acid. The mixture was heated with warm water gradually to 50°C. in around 75 minutes. Temperature was set to 16° C. Nitric acid, 31.4kg was then added gradually over a period of 3 hrs. When theadministration was complete the mixture was allowed to stir foradditional 3.5-4.5 hours.

The suspension was centrifuged whilst washed with 25 kg of acetic acid,50 liter deionised water and 25 kg of acetic acid again. The wetcrystalline material was suspended in 165 kg of acetic acid and heatedat 91° C. until complete dissolution. The solution was then cooled to19.8° C. and the mixture was allowed to stir for 1 hr. Centrifugationand washing with 15.2 kg acetic and 40 liter of deionised water wasperformed. The wet material was then dried in tray vacuum drier between40-50° C. until constant weight, for 72 hours. The dry material weightwas 28.7 kg. The calculated yield was 45.4%.

Example 1c Preparation of 4-hydroxy-5-methoxy-3 nitrobenzoic acid

A suspension of vanillic acid (68.8 kg) in acetic acid (720 kg) iscooled to 17° C. before an excess of a 65% nitric acid (44.0 kg) isadded. After complete dosage of nitric acid the suspension is stirredfor 2 hours. The suspension is filtered off and the wet cake issuccessively washed with acetic acid (80.0 kg), acetic acid/water (1:2w/w—105 kg) and finally water (80 kg—if necessary repeat). The solid isdried at 52° C. for NMT 12 hours prior going to next step.

A suspension of the crude solid (650 kg) in acetic acid is warmed to105° C. and stirred until complete dissolution of the crude solid. Afterpolish filtration, the solution is cooled to 20° C. over 3 h resultingin crystallization and the suspension is stirred for 2 h at 20° C. Thesolid is filtered off and the wet cake is successively washed withacetic acid (80 kg), acetic acid/water (1:2 w/w—105 kg) and finallywater (193 kg—if necessary repeat). 4-hydroxy-5-methoxy-3 nitrobenzoicacid pure is dried under vacuum at max. 55° C. until max 0.5% w/wresidual acetic acid and max 0.2% w/w water is reached.

Example 2a Preparation of 4-hydroxy-5-methoxy-3-nitrobenzoic acid

The process of Example 1a was scaled up to employ vanillic acid (375 g)in acetic acid (3940 g) to which was added nitric acid (65%, 245 g) at12° C. over 3 hours followed by stirring for one hour. The overall yieldwas 40% of a 99.9% pure product.

Example 2b Preparation of 4-hydroxy-5-methoxy-3-nitrobenzoic acid

Vanillic acid methyl ester (33 g) and sodium nitrite (0.625 g) arecharged. Water (158 mL) and 1,4-dioxane (158 mL) are added at roomtemperature. The reaction mixture is heated to 40° C. Nitric acid (65%)(15.75 g) is added in the course of three hours and the resultingmixture is stirred for 4 h after addition. The reaction mixture issampled for completion.

The water/nitric-acid/dioxane azeotrope is distilled off in vacuum at40° C. The resulting product suspension is quenched by addition ofsodium hydroxide solution (50%, 33.2 mL) and then stirred for 16 h. Thequench mixture is sampled for completion.

Then, HCl (18.5%, 70.2 mL.) is added until the pH is below 1. Theproduct is filtered off and washed with water (27.9 mL). The product isthen dried in vacuum at 50° C. The overall yield was 81% of a 97.3% pureproduct.

Example 3a Preparation of 4-hydroxy-5-methoxy-3-nitrobenzoyl chloride

A suspension of compound of Example 1a (1.0 eq) in dioxane (approx 4.5vol) was treated with thionyl chloride (1.5 eq) and heated to 80° C. Aclear solution formed at approximately 75° C. The mixture was stirredfor 3 hours at 80° C. Unreacted thionyl chloride was distilled off andafter distillation the residue was cooled to 10° C.

Example 3b Preparation of 4-hydroxy-5-methoxy-3-nitrobenzoyl chloride

A suspension of compound of Example 1a (1.0 eq) in DCM (approx 3.4 vol)is treated with thionyl chloride (1.0-1.2 eq, for example 1.1 eq) andcatalytic amount (0.011 eq) of DMF and the mixture is stirred for 16 hat 40° C. DCM is distilled off (approx 2.7 vol) and the residue isdiluted with THF (approx 1.8 vol). The excess of thionylchloride isdistilled off with THF/DCM and the residue after distillation is cooledto 10° C.

Example 3c Preparation of 4-hydroxy-5-methoxy-3-nitrobenzoyl chloride

A suspension of compound of Example 1a (1.0 eq) in DCM (approx 4.5 vol)is treated with thionyl chloride (1.0-1.2 eq, for example 1.1 eq) andcatalytic amount (0.0055 eq) of DMF and the mixture is stirred for 16 hat reflux. Unreacted thionylchloride is distilled off with DCM and theresidue after distillation is diluted with THF (approx 1.8 vol) andcooled to 10° C.

The amount of DCM may be approx 3.4 as an alternative to approx 4.5 vol.

The catalytic amount of DMF may be about 0.011 eq as an alternative to0.0055 eq.

Example 3d Preparation of 4-hydroxy-5-methoxy-3-nitrobenzoyl chloride

In a reactor 68 kg dichloromethane, 20 kg 5-nitro-vanillic acid ofexample 1b, 76 gram of N,N-dimethylformamide and 13.4 kg (8 L) thionylchloride, was charged at 20.2° C. The mixture was heated to 40° C. untilall the starting material dissolved and the evolution of HCl and SO₂stopped. When all the starting material was consumed 5-10 Ldichloromethane was distilled off at normal pressure at 40° C. then themixture was cooled to 20-25° C. and the distillation was continued untildry under vacuum at 40° C. The evaporation residue was dissolved in 36kg dry THF. The THF solution was used in Example 4d.

Example 3e Preparation of 4-hydroxy-5-methoxy-3-nitrobenzoyl chloride

A suspension of product of example 1C (4-hydroxy-5-methoxy-3nitrobenzoic acid —160 g, 1 eq) in 1,4-dioxane (720 mL, 4.5 vol) istreated with thionyl chloride (169.8 g, 103.7 mL, 1.5 eq) and heated to80° C. A clear solution is formed at approx. 75° C. The mixture isstirred at 80° C. (3 hours). Unreacted thionyl chloride is distilled offand the residue after distillation is cooled to 10° C.

Example 4a Preparation of5-[3-(2,5-dichloro-4,6-dimethyl-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzene

In this example the compound of formula (IV) is reacted with thecompound of formula (V) to produce the compound of the formula (III).

Compound of formula (V) (1.24 eq) was suspended in 1,4-dioxane(approximately 4.5 vol) and the suspension cooled to 10° C. The acylchloride (compound of formula (IV)) solution of Example 3a in1,4-dioxane was added slowly maintaining the temperature below 20° C. Aclear orange solution was formed. After complete addition, the reactionmixture was stirred at 20° C. for one hour. Pyridine (approximately 8eq) was added and the reaction mixture heated slowly to 115° C. Themixture was stirred for 6 hours at 115° C. and then cooled to 20° C.

The dioxane/pyridine was distilled off under vacuum at 70° C. Theresidue was kept at 80° C. and ethanol (approx 8 vol) added to inducecrystallization. The resulting yellow suspension was cooled to 0° C. andstirred for two hours. The product was filtered off and washed withethanol (2.5 vol) water (3.8 vol) and ethanol 2.5 vol). The product wasdried under vacuum at 50° C. Typical yields for this process are 82 to85%.

In an optional variant, methanol was employed in place of ethanol toinduce crystallization.

Example 4b Preparation of5-[3-(2,5-dichloro-4,6-dimethyl-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzene

In a different reactor, compound of formula (V) (1.1 eq) is dissolved inDMAc (approx 5.8 vol) and the solution is cooled to 5° C. The benzoylchloride solution of Example 3b in THF/DCM is then added slowlymaintaining the temperature below 10° C. After complete addition, thereaction mixture is stirred at 20±5° C. Pyridine (1.3 to 1.6 eq, forexample 1.5 eq) is charged and the reaction mixture is heated slowly to110±5° C. removing low boiling components by distillation. The mixtureis stirred for additional 3 h at 110±5° C.

In a further reactor, concentrated HCl (23.8 eq) is diluted with water(approx. 8.5 vol) and cooled to 10° C. The reaction mixture in pyridineis dosed slowly to diluted hydrochloric acid. After complete addition,the resulting suspension is stirred for additional 2 h and the solid isfiltered off. The crude solid is washed once with water and pre-dried onfunnel.

The crude solid is suspended in DCM (approx. 28.6 vol) and thesuspension is heated to 40° C. to reach a clear solution. Resultingsolution is cooled to 20° C. and extracted with water. After phaseseparation, the aqueous phase is re-extracted with DCM and combinedorganic phase are washed once with water. DCM is distilled off undervacuum followed by addition of ethanol. Resulting suspension is furtherdistilled to reduce the amount of DCM, then cooled to 5° C. and stirredfor additional 2 h. Finally, the product is filtered off, washed oncewith cold ethanol and dried under vacuum at 45° C.

Example 4c Preparation of5-[3-(2,5-dichloro-4,6-dimethyl-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzene

In a second reactor, compound of formula (V) (1.1 eq) is dissolved inDMAc (approx. 7 vol) and the solution is cooled to 5° C. The benzoylchloride solution of Example 3c in THF/DCM is added slowly maintainingthe temperature below 10° C. After complete addition, the reactionmixture is stirred at 20±5° C. for 30 min Pyridine (6.9 to 7.3 eq, forexample 7.14 eq) is charged and the reaction mixture is heated slowly to110° C. removing low boiling components by distillation. The mixture isstirred for additional 4 h at 110° C. and cooled to 20° C.

In a third reactor an emulsion of diluted hydrochloric acid (preparedfrom conc. HCl (19.6 eq) and approx. 7.6 vol distilled water) and DCM(approx. 25.5 vol) is cooled to about 15° C. before the reaction mixturein pyridine is dosed slowly to the emulsion. After complete addition,the organic phase is separated and washed with water before DCM isdistilled off under vacuum followed by addition of ethanol. Theresulting suspension is further distilled to reduce the amount of DCM,then cooled to 5° C. and stirred for additional 2 h.

Finally, the product is filtered off, washed once with cold ethanol anddried under vacuum at 45° C.

Example 4d Preparation of5-[3-(2,5-dichloro-4,6-dimethyl-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzene

140 kg N,N-dimethyl acetamide was charged into the reactor. 24.2 kg ofamidoxime of Preparation 4 was dissolved in N,N-dimethyl acetamide whilestirring at 21° C. The solution was cooled to 5-10° C. The THF solutionof Example 3d was introduced slowly into the reaction mixture, 1.5-2hrs, while the internal temperature was maintained at max. 9.5° C. byexternal cooling. When the addition was complete the external coolingwas stopped. The internal temperature was allowed to raise to 21° C. inan hour. After stirring for 30 minutes, pyridine 53.0 kg was added tothe mixture, while the temperature was in the range of 22.4° C.-20.6° C.Heating was started and the internal temperature raised to 105-115° C.The mixture started to reflux for 3 h while the internal temperaturemanaged to 113° C. by partial distillation of some THF. The reactionmixture was then cooled and introduced to a mixture of 220 kgconcentrated HCl and 170 kg of deionised water while the internaltemperature was maintained between 14-16° C. The reactor was rinsed with10 kg of N,N-dimethylacetamide and 20 kg deionised water. The rinseliquid was run to the mixture. The suspension was then further cooled to5-10° C. and stirred for 1.5-2.0 hours. The product was centrifuged andwas washed 80 kg deionised water. Crude wet weight of the product was88.6 kg.

The crude wet product, was dissolved in 460 kg (340 L) dichloromethaneat max 40° C. When dissolved the temperature was set to 20-30° C. and120 kg deionised water was added. The organic phase was separated, theinorganic phase was extracted with 80 kg dichloromethane. The organicphase of 460 kg, was then washed with 200 kg deionised water and thephases were separated. The inorganic phase was extracted with the 80 kgdichloromethane and the organic phases were unified. The organic phaseobtained so was concentrated in vacuum at 35° C. to 200-240 Liter, then260 kg ethanol 96% was continuously added and the evaporation wascontinued to a final 200-240 liter volume. Then the mixture was cooledto 5-10° C. and was allowed to stir for 3 hrs. Centrifuging, washingwith 20 kg ethanol resulted in 35.4 kg wet product. Vacuum drying for 16hours at 45° C. gave 34.09 kg dry product. The yield was 79.9%.

Example 4e Preparation of5-[3-(2,5-dichloro-4,6-dimethyl-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzene

In a second vessel,(Z)-2,5-dichloro-N′-hydroxy-4,6-dimethylnicotinimidamide (201.2 g, 1.24eq) is suspended in 1,4-dioxane (720 mL, 4.5 vol) and the suspension iscooled to 10° C. The residue of example 3e in 1,4-dioxane is addedslowly maintaining the temperature below 20° C. A clear orange solutionis formed. After complete addition, the reaction mixture is stirred at20° C. for 1 hour. Pyridine (483.7 mL, 8 eq) is then charged and thereaction mixture is heated slowly to 115° C. The mixture is stirred at115° C. for 6 hours. The solution is then cooled to 20° C.Dioxane/pyridine is distilled off.

After distillation, the pit is kept at 80° C. and ethanol (1.28 L, 8vol) is added at this temperature to induce crystallization. Theresulting yellow suspension is cooled to 75° C. and stirred for 1 h atthis temperature to allow crystal growth. The product suspension is thencooled to 0° C. and stirred for 2 h at this temperature. The product isfiltered off and washed subsequently with ethanol (400 mL, 2.5 vol),water (608 mL, 3.8 vol) and ethanol (400 mL, 2.5 vol). The product isdried under vacuum at 50° C. until LOD is max 1% w/w.

Example 4f Preparation of5-[3-(2,5-dichloro-4,6-dimethyl-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzene

A mixture of compound of formula (V) (11.7 g, 50 mmol, 1.25 eq), methyl4-hydroxy-3-methoxy-5-nitrobenzoate (10 g, 40 mmol, 1 eq) and acatalytic amount of p-toluenesulfonic acid (0.76 g, 4 mmol, 1 eq) indimethyl acetamide was heated to 80° C. The reaction was followed byHPLC. After 23 h, 6% of conversion was obtained.

Example 4g Preparation of5-[3-(2,5-dichloro-4,6-dimethyl-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzene

A mixture of compound of formula (V) (11.7 g, 50 mmol, 1.25 eq), methyl4-hydroxy-3-methoxy-5-nitrobenzoate (10 g, 40 mmol, 1 eq) and acatalytic amount of aluminum chloride (0.53 g, 4 mmol, 0.1 eq) indimethyl acetamide was heated to 80° C. The reaction was followed byHPLC. After 20 h, 10% of conversion was obtained.

Example 5a Preparation of5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzene

A solution of the product of Example 4a (24 g) was dissolved indichloromethane (388 g) at 20-40° C. The yellow solution was cooled to5° C. and urea hydrogen-peroxide (UHP) (17.6 g) and trifluoroacetic acidanhydride (37 g) added and stirring continued for 12 hr at 5° C. Thereaction mixture was warmed to room temperature over one hour andstirring continued for a further five hours. The precipitate that formedwas filtered off and washed with dichloromethane. The combined filtrateswere diluted further with dichloromethane, all washed and concentratedat atmospheric pressure. Toluene was added and the resulting suspensionconcentrated under vacuum, to remove residual dichloromethane. Furthertoluene was added and the mixture checked to ensure less than 0.5%dichloromethane and less than 0.1% water was present. Formic acid wasadded to provide a 10-12% formic acid in toluene mixture. The resultingsuspension was warmed to 90° C. and stirred until complete dissolutionof solid. Crude product was obtained by cooling the solution to 5-10° C.until crystallization commenced. The suspension was agitated at 5-10° C.until crystallization appeared complete. The solid was filtered off,washed with toluene and dried under a stream of nitrogen.

The crude product was suspended in 10-12% wt/wt solution of formic acidin toluene and warmed to 90° C. until dissolution of the solid. Thesolution was cooled to 5° C. and stirred at 5° C. until crystallisationoccurred. The solid was obtained by filtration and washed with toluene.This recrystallization was repeated until the product tested ascontaining less than 0.1% of starting material. The pure product wasdried under vacuum at 50° C.

Example 5b Preparation of5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzene

After dissolution of the product of Example 4b (24 g) in DCM (388 g) at20-40° C. the yellow solution is cooled to 5° C. before the temperaturecontrolled addition of urea hydrogen peroxide complex (UHP)(17.6) andtrifluoroacetic anhydride (TFAA) (37 g). After addition of TFAA iscomplete stirring is continued for 12 h at 5° C. before the reactionmixture is warmed to room temperature (RT) within 1 h and stirring iscontinued for additional 5 h. The precipitate formed during the reactionis filtered and washed with DCM on the funnel filter. The combinedfiltrates are diluted with DCM (325 g) and then repeatedly washed withwater before concentrated at atmospheric pressure. DCM is replaced bytoluene (170 g) and the resulting suspension is concentrated again undervacuum to remove surplus DCM. Distillates are replaced by fresh tolueneas before and the mixture is analyzed for residual water and DCM(Residual DCM after solvent switch max. 0.5%; residual water aftersolvent switch max. 0.1%). Formic acid (24 g) is charged resulting in anapprox. 10-12% w/w formic acid in toluene solvent mixture The resultingsuspension is warmed to 90° C. and stirred until compete dissolution ofthe solid is achieved. The crude product is crystallized by cooling ofthis solution to 5-10° C. and subsequent agitation of the resultingsuspension at 5-10° C. The solid is filtered of washed with toluene andthen dried in a stream of nitrogen gas.

The crude product so obtained is suspended in an approx. 10-12% w/wsolution (176 g) of formic acid in toluene. The suspension is warmed to90° C. and stirred until all product is dissolved. After cooling of thissolution to 5° C. and subsequent stirring at 5° C., crude product isisolated by filtration and subsequent washing of the wet product withtoluene.

The re-crystallization of crude product is repeated (2 or more times).The pure product (11.8 g) is dried at 50° C. under vacuum.

Example 5c Preparation of5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzene

After dissolution of the product of Example 4c (24 g) in DCM (388 g) at20-40° C. the yellow solution is cooled to 5° C. prior to thetemperature controlled addition of urea hydrogen peroxide complex (UHP)(17.6 g) and trifluoroacetic acid anhydride (TFAA) (37 g). Afteraddition of TFAA is complete stirring is continued for 12 h at 5° C.before the reaction mixture is warmed to RT within 1 h and stirring iscontinued for additional 5 h. The precipitate formed during the reactionis filtered and the filter cake is washed with DCM. The combinedfiltrates are diluted with DCM (325 g) and then repeatedly washed withwater before concentrated at atmospheric pressure. DCM is replaced bytoluene (170 g) and the resulting suspension is concentrated again invacuum in order to remove surplus DCM and water. Distillates arereplaced by fresh toluene followed by addition of formic acid (24 g).The resulting suspension is warmed to 80° C. and stirring is continuedin order to dissolve the solid. The product is crystallized by coolingof this solution to 5° C. and subsequent agitation of the resultingsuspension at 5° C. The solid is filtered, washed with toluene and thendried in a stream of nitrogen gas.

The product is suspended in a formic acid/toluene (18 g/158 g) mixturefollowed by warming of the reaction mixture to 80° C. After dissolutionof the product the solution is cooled to 5° C. whereby the productprecipitates. After additional stirring at 5° C. the suspension isfiltered and the filter cake is washed with toluene.

The re-crystallization of the product is repeated. The product is usedas a wet material in the next process step (12.1 g product obtained ifdried at max. 60° C.).

Example 5d Preparation of5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzene

550 kg (420 L) Dichloromethane was charged into a reactor. 34 kg ofproduct of example 4d was added to in a short period at 20° C. internaltemperature. The solution was cooled to 6.5° C. then 24.9 kg ureahydrogen peroxide complex (UHP) was added over a period of 20-40 minutesbetween 5-10° C. Stirring was continued for additional 20 minutesbetween 6.5-7.5° C. Trifluoroacetic anhydride, 53 kg, was administeredinto the reaction mixture, starting and maintaining the temperature at6-7° C. over a period of 2-3 hours. When the administration was completethe mixture was stirred for additional 30 minutes. Then the internaltemperature was allowed to rise to a maximum of 25° C. over a period of1.5 hours. The internal temperature was maintained between 20-25° C. andthe mixture was allowed to react for additional 18-20 hrs. The reactionmixture was centrifuged and the fuge was washed with 45 kgdichloromethane. To the separated dichloromethane solution 460 kg (350L) dichloromethane and 190 kg deionised water was added. The mixture wasstirred for 10 minutes and the phases were separated for 30 minutes. Theorganic phase was washed again with 2×190 kg deionised water andseparated as previously. Evaporation of the unified organic solution atmax 35° C. under vacuum was done to a final volume of 100-120 L. Then atotal of 105 kg acetonitrile was administered into the system while thedistillation was continued to keep the volume at 100-120 L. Whencomplete an additional 170 kg (220 L) acetonitrile was added to themixture at normal pressure. This suspension was heated to 70-80° C. atnormal pressure while dichloromethane was distilled off continuously.The mixture was then kept stirred for an hour. The suspension was cooledto 20-25° C. and was stirred for an additional 30 minutes. Thesuspension was then centrifuged and was washed with 30 kg acetonitrile.The wet material, 29.7 kg, was vacuum dried for 16 hrs at 30° C. Driedproduct yield was 81.5%.

27.7 kg product, 240 kg toluene and 29.2 kg formic acid was charged intoreactor then heated to 90° C. for complete dissolution for 1 hour. Thenthe solution was cooled to 7° C. and then the suspension was kept at 7°C. for additional 2 hrs. If necessary seeding was applied with 3-5 gramsof pure product. The suspension was then centrifuged for 1 hour whilstwashing with 28 kg cold toluene. The product was suspended in 225 kgtoluene and 27.2 kg formic acid was charged. The mixture then was heatedto 90° C. for complete dissolution for 1 hour. Then the solution wascooled to 20-25° C., then the suspension was kept between 15-25° C. foradditional 2 hrs, seeded if necessary. The suspension then wascentrifuged for 60 minutes whilst washed with 28 kg cold toluene. Therecrystallization process may be repeated 2-3 more times.

Drying for 24 hrs at 38-41° C. under vacuum was conducted until constantweight. This resulted in 16.34 kg (58.8%) dry material.

Example 5e Preparation of5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzene

After dissolution of the product of Example 4e (150 g) in DCM (2.43 kg)at reflux, the yellow solution is cooled to 5° C. prior to thetemperature controlled addition of carbamide peroxide (UHP—urea hydrogenperoxide) (110 g) and trifluoroacetic acid anhydride (TFAA) (155.1 ml in4 portions within 2 hours). The mixture is stirred for 12 h at 5° C.then the reaction mixture is warmed to 25° C. over 1.5 hours and stirredfor 5 hours. The precipitate formed during the reaction is filtered andthe filter cake is washed with DCM (0.36 kg). The combined filtrates arewarmed to 30° C. and diluted with water (300 g). 10% sodium hydroxide isadded until pH=4 is reached. The biphasic system is stirred for 10minutes at 30° C. and the mixture is then allowed to separate. Theorganic layer is then successively washed with a mixture water (750 g)and 10% sodium hydroxide (7.5 g) (until pH=4), 3.2% HCl solution (300g). DCM is distilled at atmospheric pressure and then replaced bytoluene (1035 g) applying vacuum (150 mbar) and keeping internaltemperature at 45° C. Formic acid (300 g) and toluene (900 g) are addedkeeping the internal temperature above 40° C. The resulting solution isdistilled under vacuum (150 mbar, 45° C. internal temperature) untildistillation ceases. After seeding at 45° C., the slurry is stirred for1 hour at 45° C. then is cooled to 5° C. over 2 hours. The suspension isstirred for at least 2 hours at 5° C. and then filtered. The wet cake iswashed with toluene (195 g) and dried in a stream of nitrogen gas(Chemical purity of crude product min. 92% area).

A suspension of crude product in formic acid (388 g, 2 wt) is warmed to55° C. and stirred until complete dissolution of the crude product.Toluene (1242 g, 6.4 wt) is added maintaining the internal temperatureabove 50° C. The reaction is stirred at 150 mBar and internaltemperature 45° C. until distillation ceases. The vacuum anddistillation is stopped and then seed is added at 45° C. The slurry isstirred for 1 hour at 45° C. and cooled to 5° C. in 2 hours. Theresulting suspension is stirred for at least 2 hours at 5° C. thenfiltered. The wet cake is washed with toluene (260 g, 1.34 wt). The wetcake is collected and charged into the reactor. This procedure isrepeated at least twice until5-[3-(2,5-dichloro-4,6-dimethyl-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzenelevel max is 0.1% (a/a) prior to dry at 25° C. max under vacuum.

Example 6

Example 5a was repeated on a larger scale employing product of Example 3(82 g), dichloromethane (1325 g), urea peroxide (60.1 g) andtrifuoroacetic acid anhydride (128 g).

Example 7a Preparation of5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-3-nitrobenzene-1,2-diol

Product of Example 6 (15 g) was suspended in N-methyl pyrrolidone (NMP)(131.5 g) and cooled to 5° C. Aluminium chloride (6.2 g) and pyridine(12 g) were added while maintaining the temperature at 5° C. After theaddition of pyridine was complete the reaction mixture was warmed to 60°C. and maintained for 2 hours. After confirmation that less than 0.5starting material remained, the reaction mixture was cooled, and aqueousHCl (water 233 g, HCl 123 g, 37%) added. The resulting yellow solid wasisolated by suction filtration. The resulting wet product was washedwith water and propan-2-ol (67 g) and dried under vacuum.

Optionally, the crude product was suspended in ethanol (492 g) andwarmed to reflux. The suspension was stirred for 1 hour under reflux andthen cooled to room temperature. The solid was obtained by filtration,washed with ethanol and dried under vacuum at 50° C. A typical yield of85% was achieved.

If desired either the final ethanol crystallised material or theinitially produced product after washing with propan-2-ol may beemployed in preparation of micronized material for use in pharmaceuticalcompositions.

Example 7b Preparation of5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-3-nitrobenzene-1,2-diol

An approx. 11% w/w suspension of the product of example 5b (20 g) in NMP(150 g) is cooled to 5° C. followed by a consecutive temperaturecontrolled addition of aluminium chloride (8 g) and pyridine (15.3 g).After addition of pyridine is complete the reaction mixture is warmed to60° C. followed by additional 2 h reaction time. After completeconversion of the product of example 5b the reaction mixture is cooledbefore an aqueous diluted hydrochloric acid (water 293 g, HCl 177 g,34%) is dosed. By addition of the hydrochloric acid, crude productprecipitates from the NMP/water matrix as a yellow solid which isisolated by suction filtration. The resulting wet product is washed withwater and 2-propanol in a replacement wash followed by drying of the wetcrude product under vacuum.

The crude product is suspended in ethanol (282 g) followed by warming ofthe mixture to reflux. The suspension is stirred for 1 h at refluxconditions followed by cooling to room temperature. The product isisolated by filtration of the suspension. The wet product is washed withethanol and subsequently dried in vacuo at approx 50° C. (typicallyweight corrected yield was 85%).

The product (20 g) is suspended in formic acid (725 g) before theresulting suspension is warmed to max. 67° C. Stirring is continueduntil complete dissolution of the product is achieved. The hot solutionis filtered and the filtrate is cooled to 40-45° C. before the productis precipitated first by concentration of the solution to approx. 40%(v/v) of its original volume followed by addition of the anti solvent2-propanol (390 g). After addition of 2-propanol is finished theresulting suspension is kept at 55-60° C. for crystal ripening followedby cooling to RT and filtration. The filter cake is washed with2-propanol followed by drying of the material at max. 58° C. until losson drying (LOD) max. 0.5%. Typically, a yield of 97-98% was obtained.

If desired the product may be employed in preparation of micronizedmaterial for use in pharmaceutical compositions.

Example 7c Preparation of5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-3-nitrobenzene-1,2-diol

A suspension of the product of example 5c (20 g) or of example 6 (20 g)in NMP (153 g) is cooled to 5° C. followed by a consecutive temperaturecontrolled addition of aluminium chloride (8.2 g) and pyridine (15.4 g).After addition of pyridine is complete the reaction mixture is warmed to60° C. followed by additional 3 h reaction time. After completeconversion of the product of example 5c or of example 6 the crudeproduct is precipitated by a temperature controlled addition of anaqueous hydrochloric acid solution (water 296 g, HCl 179 g, 34%).Filtration of the solid followed by washing of the wet filter cake withwater and 2-propanol yields a crude product wet material which isimmediately dissolved in formic acid (536 g). After polish filtrationthe filtrate is concentrated under vacuum followed by addition of theanti-solvent 2-propanol (318 g). After aging of the resulting suspensionat 55-60° C. the suspension is cooled to RT and filtered. The wet filtercake is washed with 2-propanol. The wet product is dried under vacuum atmax. 58° C. until LOD max. 0.5%. The yield was in the range of 70-95%

If desired the product may be employed in preparation of micronizedmaterial for use in pharmaceutical compositions.

Example 7d Preparation of5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-3-nitrobenzene-1,2-diol

132 kg (147 L) N-methylpyrrolidone was charged into a 1000 L reactor.16.3 kg of product of example 5d was then added. The suspension wascooled to 5-7° C. and 6.5 kg of sublimed aluminium chloride was added inportions keeping the internal temperature between 5-10° C. The mixturewas stirred for 10 minutes then 12.6 kg pyridine was added maintainingthe internal temperature between 5-10° C. The mixture was warmed withwater in the jacket to 20-25° C. and the mixture was stirred for 30minutes. Then the mixture is heated to 58-62° C. and reacted for around2 hours. In a separate reactor a mixture of 240.5 kg deionised water and146.4 kg concentrated HCl was mixed. This was cooled to 15-20° C. Thereaction mixture from the demethylation was introduced into the dilutedhydrochloric acid between 20-25° C. Optionally, 51.2 kg dichloromethanewas added to the suspension, stirred for 30 minutes and was centrifuged,washed with 60 kg deionised water and 20 kg isopropanol. Drying gave15.9 kg of product.

The product was suspended in 185.3 kg of ethanol. The mixture was thenstirred at 78° C. for an hour, then cooled to 20-25° C. and stirred for1 hour. The suspension was then centrifuged and the filtercake waswashed with 44.5 kg ethanol, 96%. The solid material was dried at 50° C.in vacuum in a stainless steel tray drier. 14.35 kg (90.3% yield) dryproduct was obtained.

A reactor was charged with 317.2 kg formic acid and dry product. Themixture was heated to 65° C. until all the solid dissolves. The hotsolution was then filtered to an empty 1000 L reactor, was rinsed with20 kg formic acid, then the formic acid solution was distilled partiallyoff under vacuum to around 80-100 L. 260 kg isopropanol was thenintroduced at 50-60° C. and stirred for 30-35 minutes. The mixture wasthen cooled to 20-25° C. with water in the jacket and was allowed tostir min 2 hours. The suspension was then centrifuged and was washedwith 25 kg isopropanol. The wet material was removed from the fuge andwas transferred into vacuum tray drier and was dried until constantweight under vacuum at 45-50° C. resulting in 13.6 kg product, with ayield of 95.3%.

If desired the product may be employed in preparation of micronizedmaterial for use in pharmaceutical compositions.

Example 7e Preparation of5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-3-nitrobenzene-1,2-diol

A suspension of product of Example 5e (34.1 kg) in N-Methyl pyrrolidone(NMP) (182 kg) is warmed to 50° C. until dissolution and then cooled to5° C. followed by a consecutive temperature controlled addition ofaluminium chloride (9.8 kg) and pyridine (18.2 kg). After addition ofpyridine is complete the reaction mixture is warmed to 60° C. andstirred for at least 2 hours. The reaction mixture is cooled to 10-16°C. (e.g. 11, 13, 15° C.) before an aqueous diluted hydrochloric acid (4Msolution, 283 L) is dosed maintaining the temperature below 25° C.During the addition of the hydrochloric acid the crude product isprecipitated from the NMP/water matrix as a yellow solid. The yellowsolid is filtered and subsequently washed with water (179 kg),2-propanol (105 kg). The wet solid is dried under vacuum at 55° C.

A suspension of wet product (25.1 kg) in formic acid (813 kg) is warmedto max. 67° C. The mixture is stirred at 67° C. until completedissolution of the product is achieved. The hot solution is filtered andthe filtrate is cooled to 40-45° C. before the product is precipitatedfirst by concentration of the solution to approx. 40% (v/v) of itsoriginal volume followed by addition of the anti solvent 2-propanol (380kg). After addition of 2-propanol the resulting suspension is stirred at55-60° C. for crystal ripening followed by cooling to RT and filtration.The filter cake is washed with 2-propanol (38 kg) and then dried at max.58° C. until LOD max. 0.5%). The product may be milled (for exampleusing the method of Example 8).

Example 8 Micronization of5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-3-nitrobenzene-1,2-diolwith MC JETMILL® type 200 milling equipment (micronization throughspiral jet mills) Equipment: Mill: MC JETMILL® 200

Dosing unit: K-Tron T 35Cyclone: type 600

Each micronization trial was performed on at least 2 kg of5-(3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-3-nitrobenzene-1,2-diol.

The following working parameters have been defined for themicronization:

Feed rate range: 24.0-48.0 kg/h (200-400 g/30 sec.)Mill pressure range: 3.0-4.0 barVenturi pressure range: 3.0-4.0 bar; preferably the Venturi pressure isthe same as the mill pressure

Using the above equipment and working parameters the microparticles of5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-3-nitrobenzene-1,2-diolcomply with the following particle size specification (particle sizedetermined by optical microscopy): D10 (EDC) is not less than 4 or 5 μm(for example not less than 5 μm), the D50 (EDC) is 10-45 or 15-30 μm(for example 15-30 μm) and the D95 (EDC) is not more than 60 or 70 μm(for example not more than 60 μm).

Example 9 FIG. 5

2,5-Dichloro-4,6-dimethyl-nicotinonitrile is reacted with hydroxylaminein the presence of catalytic amounts of 1,10-phenanthroline monohydrateto yield the aldoxime(Z)-2,5-dichloro-N′-hydroxy-4,6-dimethylnicotinimidamide whichrepresents the first coupling partner towards the synthesis of5-[3-(2,5-dichloro-4,6-dimethyl-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzene.The second coupling partner 5-nitro-vanillic acid pure is synthesizedfrom vanillic acid by nitration with 65% nitric acid followed byre-crystallization of the crude 5-nitro-vanillic acid intermediate fromacetic acid. The convergent assembly of the oxadiazole moiety in5-[3-(2,5-dichloro-4,6-dimethyl-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzeneis achieved by first activation of 5-nitro-vanillic acid as its acidchloride and subsequent coupling with the aldoxime(Z)-2,5-dichloro-N′-hydroxy-4,6-dimethylnicotinimidamide. Cyclisation ofthe initially formed coupling product is achieved thermally to give theoxadiazole moiety by elimination of water. The reaction mixture of5-[3-(2,5-dichloro-4,6-dimethyl-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzene,after ring closure reaction, is concentrated and product isolated from1,4-dioxane/ethanol mixture in one step. Oxidation of the pyridine ringto the corresponding aryl-N-oxide(5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzene)is achieved with trifluoroperoxoacetic acid which is formed in situ fromUHP (Urea hydrogen peroxide complex) and trifluoroacetic acid anhydride.Unreacted5-[3-(2,5-dichloro-4,6-dimethyl-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzeneis subsequently removed from5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzeneby repeated re-crystallisation from formic acid/toluene. The analogueintermediate5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzenepure with a level of5-[3-(2,5-dichloro-4,6-dimethyl-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-2-hydroxy-3-methoxy-1-nitrobenzenebelow 0.10% area is converted to5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-3-nitrobenzene-1,2-diolcrude analogue by ether cleavage in the presence of a stoichiometricamount of aluminium chloride and pyridine. After completion of thereaction, the crude product is isolated by precipitation with an aqueoushydrochloric acid followed by dissolution of the precipitate in formicacid. After polish filtration of the resulting solution and partialsolvent switch from formic acid to isopropanol,5-[3-(2,5-dichloro-4,6-dimethyl-1-oxy-pyridin-3-yl)-[1,2,4]oxadiazol-5-yl]-3-nitrobenzene-1,2-diolis crystallized from the resulting formic acid/IPA crystallizationmatrix and finally optionally milled to the desired particle size.

1. A compound of the formula (I)

or a salt thereof.
 2. A compound as claimed in claim 1 in crystallineform.
 3. A compound as claimed in claim 1 in an organic solvent.
 4. Acompound as claimed in claim 3 wherein the organic solvent is N-methylpyrrolidone.
 5. A method of preparing a compound of the formula (II)

or a salt thereof which comprises O-demethylation of a compound of theformula (I) as set forth in claim 1 or a salt thereof.
 6. A method asclaimed in claim 5 wherein the demethylation is effected by reactionwith a Lewis acid, such as aluminium chloride, and a base such aspyridine.
 7. A method as claimed in claim 6 wherein the demethylation iscarried out in solution in N-methyl pyrrolidone.
 8. A method as claimedin any of claims 5 to 7 performed at 45° C. to 70° C.
 9. A method asclaimed in claim 8 performed at 55° C. to 65° C.
 10. A pharmaceuticalcomposition in unit dosage form for oral administration which comprisesa compound of the formula (II)

in microparticulate form in a pharmaceutically acceptable carriertherefore.
 11. A pharmaceutical composition as claimed in claim 10wherein the microparticles of compound of formula (II) are produced byball milling or by micronization through spiral jet mills.
 12. A methodas claimed in any of claims 5 to 9 wherein the compound of formula (I)or salt thereof is prepared by the oxidation of a compound of formula(III)

or salt thereof.
 13. A method as claimed in claim 12 wherein theoxidizing agent is H₂O₂.
 14. A method as claimed in claim 13 wherein theH₂O₂ is H₂O₂-urea addition complex.
 15. A method as claimed in either ofclaim 13 or 14 carried out in solution in methylene chloride to thepresence of trifluoroacetic anhydride.
 16. A method as claimed in any ofclaims 12 to 15 wherein the compound of the formula (III) is prepared bythe reaction of the compound of formula (IV)

wherein Y is a halo group, such as chloro, or OR, in which R is hydrogenor a C1-C6 alkyl such as methyl or ethyl, with a compound of formula (V)


17. A method as claimed in claim 16 wherein Y is chloro and the compoundof the formula (IV) has the formula (VIII):


18. A method as claimed in claim 16 wherein Y is OR and R is hydrogenand the compound of formula (IV) has formula (VI):


19. A method as claimed in claim 18, wherein the reaction includes theaddition of a coupling reagent.
 20. A method as claimed in any of claims16 to 19 wherein the reaction of the compounds of formula (V) andformula (IV) takes place in a mixture of dimethylacetamide,tetrahydrofuran pyridine, or in dioxane in presence of pyridine.
 21. Amethod as claimed in claim 20 wherein the reaction is performed at atemperature of 100° C. to 120° C.
 22. A method as claimed in claim 21wherein the reaction is performed at 105° C. to 115° C.
 23. A method asclaimed in any of claims 16 to 21 wherein, following reaction of thecompounds of formula (IV) and formula (V), ethanol is added to themixture.
 24. A method as claimed in any of claims 12 to 22 wherein thecompound of formula (III) is oxidized to the compound of formula (I)without isolation or purification following the reaction of compounds offormula (IV) and formula (V).
 25. A method as claimed in any of claims12 to 24 wherein the compound of formula (I) is crystallised from anorganic solvent.
 26. A method as claimed in claim 25 wherein the organicsolvent is a mixture of toluene and formic acid.
 27. A method as claimedin any of claims 12 to 26 wherein the compound of formula (II) iscrystallised from an organic solvent.
 28. A method as claimed in claim27 wherein the solvent is a mixture of propan-2-ol and formic acid. 29.A method as claimed in any of claims 12 to 28 wherein the compound offormula (VIII) is prepared from the compound of the formula (VI)

by reaction with SOCl₂ in dioxane at 75° C. to 85° C. or with SOCl₂ inDCM with DMF as catalyst.
 30. A method as claimed in claim 29 whereinthe compound of formula (VI) was prepared by the nitration of vanillicacid with 65% HNO₃ in acetic acid or by the nitration of methylvanillate with 65% HNO₃ in dioxane/water, followed by the hydrolysiswith sodium hydroxide
 31. A method as claimed in any of claims 12 to 30wherein the compound of formula (V) is prepared from the compound of theformula (VII)

by reaction with hydroxylamine in the presence of 1,10-phenanthrolinemonohydrate.
 32. A method as claimed in claim 31 wherein the reaction iscarried in a mixture of methanol and water at 70-80° C.
 33. The compoundof formula (II) as shown in claim 5 in crystalline form.
 34. Thecompound of claim 33 for use in the treatment of Parkinson's disease.35. The compound for use of claim 33 wherein administration is oral. 36.A method of treating Parkinson's disease in a patient sufferingtherefrom which comprises administering to the patient and effectiveamount of levodopa, a peripherally selective aromatic amino aciddecarboxylase inhibitor and the compound of claim
 33. 37. A method asclaimed in claim 36 wherein the administration of each of levodopa, theperipherally selective aromatic amino acid decarboxylase inhibitor andthe compound of claim 33 is oral administration.